Biological evolution is controversial, but it at least has the imprimatur of science. The same cannot be said for all the ways in which evolution has infected our thinking about everything from sociology to economics. For example, it has become common to refer to almost any kind of progress as evolution. We might talk about the evolution of the computer or the evolution of a software application. In doing so, we tacitly remove intelligent intention from the understanding of progress. Evolution purports to describe a process by which all living things arose from inanimate matter with only three principles to drive it: 1. sufficient time (billions of years) to make highly improbable events likely, 2. a mechanism of variation (mutation), and 3. a mechanism to drive toward increasing complexity (natural selection). There is no intelligence (or at most a very minimal intelligence) in this process and certainly no intention.
Proponents of intelligent design don’t find these three principles sufficient. It’s not hard to see why. The first principle is not controversial. If I flip a coin 20 times, the chances that it will come up heads every time are a bit less than one in a million. If I flip a coin 1,000,000 times, though, the chances of having a string of 20 heads somewhere in there is a bit more than 60%. If I flip the coin billions of times, the chances of a string of 20 heads approaches certainty. The probability of life arising from non-living matter is considerably smaller by several orders of magnitude. Scientists have been unable to produce any self-replicating organisms from lifeless matter despite doing their best to stack the odds in their favor.
Mutation is also not controversial. Everyone agrees that mutation occurs, and has a variety of causes. There is one little sticking point, however. Nearly all mutations that we have been able to cause or observe make a species less likely to survive, not more likely. The odds against a variation caused by mutation being useful are very high, and they become higher still the more complex the organism is. Moreover, in mammals at least, mutations that significantly alter an individual often leave it sterile. Mutation may be necessary for evolution, but it hardly seems sufficient to expalin the actual diversity of life.
Natural selection is by far the most controversial and least observable of the drivers for evolution. The idea seems simple enough. Individuals well-suited to their environment will thrive and reproduce. Ill-suited individuals will die, and with them the genes that make them ill-suited will be lost. One commonly cited example is that of the peppered moth. During the industrialization of Britain, pollutants darkened the trees where the peppered moth commonly rested. Most moths were light colored, and birds could easily spot them against the soot-stained bark of the trees. After a few years, most peppered moths were dark; the light variety had all but vanished. As time passed, Britain cleaned up its pollution. The trees were no longer stained by soot, and the bark became lighter. The color of the moths changed again from dark to light.
The problem with this example is twofold. It does not demonstrate a change in the genetic makeup of peppered moths, only in the characteristics of a population. Nor does it provide the kind of dramatic change that must occur for natural selection to be a sufficient driver for evolution.